The invention relates to a process for the catalytic hydrogenolysis of glycerol. In particular, the invention relates to the preparation of propylene glycols (1,2- and 1,3-propanediols) and/or acrolein by the hydrogenolysis of glycerol.
Propylene glycols and acrolein are valuable chemicals. For instance, 1,3-propanediol (PDO) is an attractive monomer in the preparation of polyesters and polyurethanes. It may also be used to prepare cyclic ethers that find use as solvent. Likewise, acrolein and its dimer provide a valuable starting point for the synthesis of chemicals used in textile finishing, paper treating, and the manufacture of rubber chemicals, pharmaceuticals, plasticizers and synthetic resins. Propylene glycols and acrolein may be prepared by a variety of processes. For example, PDO may be prepared by the hydroformylation of ethylene oxide, or by the hydrogenation of 3-hydroxypropionaldehyde. However, each of these processes requires chemicals as starting point that have to be prepared separately, often at considerable costs. Besides, the starting chemicals may find other higher-value uses.
The chemicals industries have realised that our petrochemical resources are not unlimited. Therefore, they focused and still focus on natural resources as starting point for their processes. For instance, U.S. Pat. No. 4,642,394 describes the process for the conversion of glycerol to lower oxygenated hydrocarbons, such as 1,2- and 1,3-propanediol, by reacting glycerol with carbon monoxide and hydrogen (in a "hydrogenolysis" reaction) in the presence of a homogeneous catalyst containing tungsten and Group VIII metal components. The examples of this patent document, however, reveal the need for elevated temperatures and pressure conditions (200 centigrade, 4600 psig). The process is therefore not quite as attractive as it could be.
The art also includes examples of hydrogenolysis processes using heterogeneous catalysts. For instance, DE-A-4,302,464 describes the conversion of glycerol into 1,2-propanediol and other products (but not 1,3-propanediol) using copper chrome tablets at various elevated temperatures and pressures. U.S. Pat. No. 5,326,912 employs a catalyst containing ruthenium, palladium and copper. However, glycerol is produced rather than converted.
It is therefore an object of the invention to provide a process for the conversion of glycerol to lower oxygenated hydrocarbons which avoids the need for these elevated temperature and pressure conditions.